Precise openings (windows, doors )in meshes
You can use snapping limiting transforms on an axis.

Basic house with a separate window object :


Select your house, enter in edit mode (tab)
Activate snapping, open the menu and choose Vertex :


Add your edge loop (Ctrl+R) place it anywhere. Move your newly created edge loop with g, lock your movement on X axis (X) and move your mouse close to a corner of your window. You'll see a circle appear where the movement can be snapped (window corner vertex). Click LMB


Repeat this actions on the 3 other loops with the 3 other corners (X and Z axis)


You can move along all axis, 1 axis (with X, Y or Z) or 2 axis (with Shift+X all but X, Shift+Y all but Y, Shift+Z all but Z).